Paste in your list of gene symbols, annotation IDs, refSeq IDs or FBgn IDs and convert!
Note: It is not possible to convert Flybase IDs to refSeq IDs since refSeq IDs are transcript IDs, whereas Flybase IDs are gene IDs. So for a given gene, there could be multiple transcripts, resulting in one FBgn ID to many refSeq IDs.